This invention is concerned with apparatus for use in the manufacture of glassware articles and with a method of controlling such apparatus.
A conventional apparatus for use in the manufacture of glassware articles comprises a furnace in which raw materials are melted to form molten glass, a forehearth channel through which molten glass flows out of the furnace, a feeder associated with the forehearth and operable to form molten glass in the forehearth into discrete gobs which fall from the feeder, a gob distributor arranged to distribute gobs falling from the feeder to the sections of a glassware forming machine of the individual section type of the apparatus, a control system for the glassware forming machine operable to control the timing of the operation of components of the sections of the machine in timed relationship to one another so that gobs received are formed into articles of glassware which are deposited on a deadplate of the section, and pusher means associated with each section of the machine operable to push articles from the deadplate of the section onto a conveyor of the apparatus which runs past the deadplates of all the sections. A glassware forming machine of the individual section type comprises a plurality of independent glass manufacturing units, called "sections", each of which operates to manufacture gobs of molten glass into articles of glassware. The sections operate under the control of the control system therefor, which is usually an electronic control system, to form gobs into articles of glassware with the sections operating with phase differences between them related to the intervals at which gobs are produced by the feeder so that, at any given time, each section is at a different stage of its operation from all the others.
In a conventional apparatus as described above, the feeder is operated by an AC electric motor driving a cam, which causes movement of a plunger surrounded by a tube of the feeder which opens and closes at least one orifice in the bottom of the channel to allow glass to flow through the orifice, and a further cam which controls the action of shears which shear the glass flowing through the orifice into gobs. A timing signal for the control of, the remainder of the apparatus is taken from the shaft of the feeder and fed to the electronic control system for the glassware forming machine so that the machine is operated in synchronisation with the action of the feeder. The gob distributor of a conventional machine comprises at least one gob-delivering scoop which is moved to align with gob-delivering guides of the various sections. The gob distributor is driven by an AC electric motor which operates a cam which causes the scoop to be aligned with the sections in a predetermined sequence. The frequency of the electric power supplied to the motor of the gob distributor is related to the frequency of the supply to the motor of the feeder so that the gob distributor operates in synchronisation with the operation of the feeder to distribute the gobs supplied by the feeder to the appropriate sections of the machine. The pusher means associated with the sections of the machine are operated by a common AC motor which drives a shaft on which one cam for each section is mounted to operate the pusher means of that section. The frequency of the power supplied to the motor of the pusher means is related to that supplied to the motors of the feeder and the gob distributor so that the pusher means operates in synchronisation with the feeder and the gob distributor and with the operation of the sections of the machine. The position of the cams on the shaft determines the order of the operation of the pusher means of the sections, the order being in most cases the same as the predetermined order of gob supply by the gob distributor. The conveyor of a conventional machine is also operated by an AC motor so that the speed of the conveyor depends on the frequency of the electric supply to the motor and this frequency is related to that supplied to the feeder, the gob distributor, and the pusher means so that the conveyor runs at an appropriate speed to collect all the articles formed by the machine.
In a conventional apparatus, it is possible to speed up or slow down the operation of the apparatus by altering the frequency of the power supply to the various AC motors. However, the characteristics of a particular article being manufactured determine to what extent the apparatus can be so speeded up or slowed down. In the operation of the glassware forming machine, a certain amount of heat has to be extracted from the glass to enable the article to be successfully formed and sufficient time has to be available for this heat extraction to occur. On the other hand, the glass must not be allowed to cool so much that the glass cannot be formed. The amount of time which is required depends on the characteristics of the glass used in the apparatus, the weight of the article being manufactured, the surface area of the article, and in some cases, on the shape of the article being manufactured. In general, it is only possible to speed up or slow down the apparatus by approximately 2%.
Clearly, an apparatus of the type described cannot be operated so that a greater quantity of glass is used by the machine than can be melted by the furnace. The quantity used by the machine depends on the number of sections the machine has, the number of moulds which are used simultaneously in each section (it being common practice to use two or more moulds in each section so that each section operates on two or more gobs simultaneously), and on the weight of the article being manufactured. The only variable factor among these factors in a conventional apparatus is the speed of the machine which, as aforementioned, can only be adjusted within a narrow range. Thus, with a conventional apparatus it is seldom possible to match the melting capacity of the furnace to the glass usage by the machine. This is an undesirable situation because, as it is necessary to maintain the glass in the furnace at a constant level to ensure constant flow conditions from the furnace into the forehearth, heat losses from the furnace are substantially constant whatever the glass usage and form a considerable expense. Thus, if a furnace is used at substantially below its full melting capacity the heat losses are more significant when considered in terms of the number of saleable articles produced. The desirable situation that the glass usage substantially equals the melting capacity of the furnace is seldom, if ever, achieved with conventional apparatus.
It is an object of the present invention to provide an apparatus of the type described in which the melting capacity of the furnace can be more fully utilised than is generally the case with conventional apparatus.